Description
Osteocephalus vilarsi is a medium-sized member of the O. planicepsspecies group. Originally only known from the holotype, the species was rediscovered in 2019 and its range was expanded. The species has a male snout-vent length range of 47.5 – 58.4 and a female range of 54.6 - 65.3 mm (Ferrão et al. 2019). The body is wedge shaped and depressed with a relatively large, depressed head (Melin 1941). The snout is slightly longer than wide, shorter than the eye diameter, round in the lateral view, and truncate in the dorsal view (Melin 1941, Ferrão et al. 2019). The elevated nostrils are close to the tip of the snout and directed laterally (Melin 1941, Jungfer 2010). The canthus rostralis is medially curved, but otherwise straight, sharply angular, and elevated. The loreal region is concave (Melin 1941, Ferrão et al. 2019). The eyes are prominent and extend beyond the lateral margins from the dorsal view (Melin 1941). The pupil is oval (Ferrão et al. 2019). The interorbital space is wider than the upper eyelid (Melin 1941). Adults in the species are characterized by well-marked but low frontoparietal ridges (Ferrão et al. 2019) that are arranged in almost parallel ridges (Jungfer 2010). The conspicuously large horizontally elliptical tympanum is 64 – 76% of the eye diameter with a distinct tympanic annulus. There is also a well-developed supratympanic fold (Ferrão et al. 2019) along the anterior edge of the tympani that extends to the upper edge of the arm insertion (Jungfer 2010). Males have vocal slits and sacs. The distinct sac is subgular with moderate expansion in the area between the tympanum and the forearm insertion (Ferrão et al. 2019).

Adult males have conspicuous tubercles on their dorsal surface while females have numerous low minute tubercles. In breeding males, the dense protuberant tubercles have keratinized spinous tips (Ferrão et al. 2019). The loreal region is graunlated. The skin above the sphenethmoid is loose. The ventrum is smooth at the thorax and chin. The belly and posterior two-thirds of the thighs are granulated (Jungfer 2010). The holotype had a prominent longitudinal furrow at the shoulder and an indistinct transverse fold along the chest. The side of the body is areolate with furrowed pleats on the posterior region (Melin 1941). The cloaca opening is at approximately three-fourths of the thigh height (Jungfer 2010).

The limbs are long (Melin 1941). The arms have a low ulnar tubercle. An axillary membrane is present. The hands have basal webbing with a formula of II (2 – 2+) - 3+ III (3 – 3) — (3 – 3) IV (Ferrão et al. 2019) and the relative finger lengths are I < II < IV < III (Jungfer 2010). There is a large elliptical thenar tubercle at the thumb. The subarticular tubercles are small and tooth-like (Melin 1941), except for finger IV, which has a bifid distal subarticular tubercle (Ferrão et al. 2019). There are also supernumerary tubercles near the proximal subarticular tubercles and a few low tubercles present on the outer edge of Finger IV (Jungfer 2010). The discs are small, about half the size of the tympanum and oblong (Melin 1941). Breeding males do not have subdigital nuptial excrescences but do have nuptial excrescences that cover the callus-like, inner prepollex and extend laterally to the thumb disc (Ferrão et al. 2019).

When extended along the body, the tibio-tarsal articulation of the hindlimb reaches the tip of the nose. The tibia is longer than the thigh. There is no tarsal fold . The foot has a low tarsal tubercle, a large, elliptical inner metatarsal tubercle, and an indistinct outer metatarsal tubercle (Melin 1941).The subarticular tubercles of the toes are single and conical. The proximal segments of toes III - V have many supernumerary tubercles (Jungfer 2010). The toes have three-fourths toe webbing with a formula of I (1+ – 1 1/2) — ( 1 1/2 – 2+) II (1 – 1+) — (1 1/2 – 2+) III (1 – 1+) — (2− – 2 1/2) IV (1 1/2 – 2−) — (1 – 1+) V and a relative toe length of I < II < III < V < IV (Ferrão et al. 2019). Like the fingers, the toes have small, oblong discs (Melin 1941).

At Gosner stage 36, tadpoles have a total length range of 33.0 – 34.5 mm. The body length is 44 – 50% of the tail length and the maximal body height is smaller than the maximal tail height. In the lateral view, the body is compressed while in the dorsal view it is ovoid. In both the lateral and the dorsal views, the snout is rounded. The anterolaterally directed, circular nostrils are located dorsolaterally. The internarial distance is smaller than the interorbital distance. The eyes are directed and located dorsolaterally. The oral discs is directed and located anteroventrally. The oral disc is large and has protuberant labia with long, cylindrical marginal papillae surround all but approximately a third of the anterior medial region of the disc. On the upper labium, there are one to three rows of papillae at the central and posterior portions. On most of the lower labium there are two rows of papillae, except at the corners where there are three. The labial keratodont row formula is 2(2)/5 – 6(1). The second anterior row and the first posterior row have small gaps with the anterior gap being larger than the posterior. The upper jaw sheath is slender, finely serrated, and arc-shaped. The V- shaped lower jaw sheath is also slender and finely serrated. The tapdpoles have a single, sinistral spiracle that has a free inner wall. In the lateral view, the distal portion of the spiracle extends beyond the outline of the tail. The vent tube is dextral and is attached to the ventral fin with the right wall positioned dorsally. The dorsal and ventral fins of the tail are equal in height. The ventral fin does not extend past the lower margin of the body. There are no flagellum (Ferrão et al. 2019).

Osteocephalus vilarsi can be differentiated from other members of the the O.planiceps species group, which includes O. castaneicola, O. deridens, O. fuscifacies,O. leoniae,and O. planiceps, by morphology and advertisement call. More specifically, O. vilarsiis distinguished from O. castaneicolaby the focal species having a truncated snout in the dorsal view, vocal slits, distinct vocal sacs in the subgular region, and a bifid distal subarticular tubercle under Finger IV. Osteocephalus vilarsi has a larger snout-vent length, more tuberculated skin, and white tibiofibular bones in comparison to O. deridensand O. fuscifacies. In O. vilarsi, the relative toe length of toe III is less than toe V, the upper part of the iris is dark brown with incomplete fine dark brown radiation, and the tibiotibular bones are white, which differentiate it from O. leoniae. From O. planiceps, O. vilarsican be differentiated by the latter being smaller, having white tibiofibular bones instead of green, and from the structural and temporal patterns of advertisement call. The calls of O. vilarsi include two- and three-note calls. The first note is shorter and always composed of two pulses in O. vilarsi vs. a single pulse in O. planiceps. Additionally, metamorphic O. vilarsican be differentiated from O. planiceps by the former having an entirely bright red iris that lacks black reticulations (Ferrão et al. 2019).

Osteocephalus vilarsihas historically been mis-identified with members of the O. taurinus(O. oophagusand O. taurinus) and O. leprieurii (O. leprieurii and O.yasuni) species group. Osteocephalus vilarsi can be differentiated from the O. taurinusspecies group by the former’s bicoloured iris that is bright gold above with dark brown veins and fine incomplete dark brown radiation and silver to with dense dark brown veins and/or incomplete radiation below, by white tibiofibular bones, and by males having a distinct vocal sac. Metamorphic O. vilarsilack reddish orange blotches on hand, elbow, knees, discs and heels that differentiate it from O. taurinusspecies group members (Ferrão et al. 2019). Specific to O. taurinus, a more angular canthus rostralis, a straight supratympanic fold, smooth anterior dorsum, and bifid subarticular tubercle on Finger IV in O. vilarsi differentiate the two (Jungfer 2010)

From members of the O. leprieurii species group, O. vilarsi can be differentiated by the latter having frontoparietal ridges, lacking subdigital nuptial excrescences, and a distinct vocal sac in the subgular region. Metamorphic O. vilarsi have a grey dorsum with darker grey blotches and a bright orange iris that differentiate it from the other members of the O. leprieuriispecies group (Ferrão et al. 2019).

Osteocephalus vilaristadpoles at Gosner stage 36 can be differentiated from O. oophagusby geography, total length, having a rounded snout in the dorsal view, and having more lower tooth rows. At Gosner stages of 45 and greater O. vilariscan be differentiated from other species in the O. planicepscomplex by the presence of grey blotches and spots on the dorsum and flanks (Ferrão et al. 2019).

In life, adult specimens are pale brown, yellowish brown to reddish brown dorsally, with or without a pattern of dark brown to black irregular markings; interorbital stripe and dark brown canthal stripe present; a narrow pale supralabial line expanding in a subocular spot; flanks creamy to yellowish white, with or without irregular brown markings or small spots; hidden thigh surfaces light brown; throat and belly creamy or yellowish white with or without diffuse small pale brown markings or spots; a narrow dark line present along the mandible; ventral thigh surfaces fleshy pink to slightly orange; iris bicolored with a dark brown horizontal stripe, bright golden above with dark brown veins and fine incomplete dark brown radiation, silver to bronze below with dense bold dark brown veins and/or incomplete radiation. The nuptial excrescences are dark (Ferrão et al. 2019).

In preservative, the dorsum is a uniform reddish brown. The upper eyelids and sides of the head darkish brown. There is a narrow dark band below the rostral edge that extends as a broader light-edged one through the eye and tympanum to the base of the forelimb and continue along the sides as a line of black spots. The sides of upper jaw are whitish with traces of dark cross bars, including a distinct one under the eye. The sides of the body are darkish with black spots and are often marbled with the whitish background. The thighs, tibiae, and tarsi have two broad, light-edged, dark cross bars on a brownish ground. This patterning is less distinct on the thighs. The sides of the thighs are finely mottled with brown. The ventrum is whitish with small, dark, sparse spots along the jaw, on the chest, and on the sides (Melin 1941).

In life, at Gosner stage 36 tadpoles have a light brown dorsum with irregularly distributed dark brown spots. There is a dark brown band from the nostril to the anterior portion of the orbits. The iris is black with a red ring around the pupil. The ventrum is translucent. The dorsal portion of the tail musculature is bronze while the ventral portion is pinkish cream. The fins are translucent with light brow blotches (Ferrão et al. 2019).

Tadpoles at Gosner stage 39 – 40 have a similar color pattern, except that the dorsum color and fin blotches become darker and there is a large cream blotch on the knee and heel. However, tadpoles at Gosner stage 45 have a silvery cream dorsum with dark and light grey blotches and spots. They also have a dark grey band extending over the lateral region of the head, from the snout to the posterior portion of the tympanum and on the upper lips. The iris is black with a red ring around pupil. The fingers, hands, forearms, toes and feet are grey. The upper arm is white and there are white blotches on the knee and heel. The groin is light grey the tail is dark grey and the venter is white (Ferrão et al. 2019).

In life, metamorphs have a grey dorsum with dark grey blotches. On the interorbital region, they have a large dark grey band. The subocular region is white and extends to the anterior infratympanic area. A dark stripe covers the supratympanic region, from the posterior corner of the eyes to the arm insertion. The iris is bright red and the pupil is black. The limbs are grey, except for the upper arm, which is white. There are four transversal dark grey stripes on the thigh, and three horizontal dark grey stripes on the forearm and tarsus. There is also a light grey blotch on knee and a white blotch on the heel. The ventrum is white (Ferrão et al. 2019).

In addition to the presence of vocal slits, vocal sac, and dark keratinous nuptial excrescences in males, O. vilarsi exhibits sexual dimorphism of body size and dorsal skin texture. Adult males possess numerous protuberant spinous tubercles distributed on the dorsal surfaces of the head, body and limbs. Dorsal tubercles in adult females are minute and flat (Ferrão et al. 2019).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Brazil, Colombia

View distribution map in BerkeleyMapper.

Osteocephalus vilarsi is widely distributed in North-western Brazil (inside the interfluve between the Negro and Solimões rivers, as well as at the left bank of the upper Negro River; state of Amazonas) and the adjacent Southern Venezuela. It is expected in Colombia (Ferrão et al. 2019).

Osteocephalus vilarsi exhibits a strong ecological association to white-sand ecosystems (e.g. primary and secondary white-sand forests, as well as ecotonal zones between white-sand forests, igapó and terra firme forests). The species was recorded both in relatively undisturbed forests and in heavily altered habitats adjacent to communities and farmlands. In the vicinity of the municipality of Novo Airão (Amazonas, Brazil) it was found both in the semi-open white-sand forest known as campinarana (canopy below 20 m) and in high closed forests (canopy above ca. 20 m) (Ferrão et al. 2019).

Life History, Abundance, Activity, and Special Behaviors
It appears that O. vilarsi can breed in small water bodies (e.g. small temporary puddles, phytotelmata) both in closed and in open forests. At Jaú National Park, individuals were found from the ground to 1 m above the ground on shrubs in open white-sand forests with canopy below 10 m. Breeding sites were near or above temporary puddles (Ferrão et al. 2019).

Two male O. vilarsi were observed calling on 24 - 26 October 2017 in the Rio Negro Sustainable Development Reserve. Males were observed calling from the same location over multiple nights. Some males also altered their vocalization in response to playbacks, indicating territorial behavior (Ferrão et al. 2019).

The advertisement calls of O. vilarsi have a duration of 144 - 337 ms and consists of two to three notes. The first note is shorter and always composed of two pulses in O. vilarsi. The second and third consist of one or two pulses. The note durations can last from 36 - 116 ms while the internote interval lasts from 39 - 73 ms. The overall dominant frequency ranges from 474 - 948 Hz, however, the first pulse has a dominant frequency of 560 - 948 Hz, the second pulse ranges from 474 - 689 Hz (Ferrão et al. 2019).

Breeding sites are also used by members of the Rhinella margarititera species group (Ferrão et al. 2019).

Tadpoles can be found in shallow puddles that are isolated from streams (Ferrão et al. 2019).

Trends and Threats
Because of the species' narrow ecological preference to white-sand forests, O. vilarsi is threatened by habitat loss (Ferrão et al. 2019).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities

Comments
The species authority is: Melin, D. E. 1941: Contributions to the knowledge of the Amphibia of South America: Göteborgs Kungl. Vetenskaps-och Vitterhets-samhälles. Handlingar. Serien B, Matematiska och Naturvetenskapliga Skrifter 1:1–71.

Based on Bayesian Inference of five mitochondrial markers (12S, 16S, COI, CYTB, ND1; 4382 bp), O. vilarsi is most closely related to the clade composed of O. deridens, O. fuscicacies and O. leoniae. These species together are sister to O. planiceps. Osteocephalus castaneicola has a basal relationship to the rest of the O. planiceps members (Ferrão et al. 2019).

References

Ferrão, M., Moravec, J., Moraes, L. J. C. L., de Carvalho, V. T., Gordo, M., Lima, A. P. (2019). ''Rediscovery of Osteocephalus vilarsi (Anura: Hylidae): an overlooked but widespread Amazonian spiny-backed treefrog.'' PeerJ, 7, e8160. [link]

Jungfer, K.-H. (2010). ''The taxonomic status of some spiny-backed treefrogs, genus Osteocephalus (Amphibia: Anura: Hylidae).'' Zootaxa, 2407, 28–50. [link]

Melin, D. E. (1941). ''Contributions to the knowledge of the Amphibia of South America: Göteborgs Kungl.'' Vetenskaps-och Vitterhets-samhälles. Handlingar. Serien B, Matematiska och Naturvetenskapliga Skrifter, 1(4), 1–71.

Species Account Citation: AmphibiaWeb 2020 Osteocephalus vilarsi <https://amphibiaweb.org/species/7475> University of California, Berkeley, CA, USA. Accessed Nov 21, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 21 Nov 2024.

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